Fibromyalgia is a disease characterized by generalized musculoskeletal pain, with excessive hypersensitivity at multiple predefined points, without demonstrable organic alterations.
At times fibromyalgia has been related to the Chronic Fatigue Syndrome, with which it shares some similarities. However, and in spite of the fact that at times patients who suffer from the one may also suffer from the other, these diseases are clearly differentiated by the World Health Organization classification of diseases.
The current fibromyalgia diagnosis [World Health Organization (WHO) code M79.0 in the International Classification of Diseases manual (ICD-10)] is based on a clinical examination of the following eight symptoms:                Difficulty thinking clearly        Throat irritation        Hypersensitivity of the lymph nodes        Muscular pain        Joint pain        Headache        Sleep disturbance        Discomfort for more than 24 hours after strenuous effort        
According to the criteria established by the American College of Rheumatology (ACR), a person suffers from fibromyalgia if they present with a history of generalized pain for a minimum of three months, as well as pain in 11 or more of the 18 specific areas of hypersensitive points (areas of the body that are painful when pressure is applied thereto).
In an attempt to standardize the physical examination performed by psychometric questionnaires are also used, which include:                a) Fibromyalgia Impact Questionnaire (FIQ) (Rivera J, Gonzalez T, “The Fibromyalgia Impact Questionnaire: a validated Spanish version to assess the health status in women with fibromyalgia”, Clin Exp Rheumatol., 2004 September-October, 2285):554-60; Burckhardt C S et al., “The fibromyalgia impact questionnaire: development and validation”, J Rheumatol. 1991, 18(5):728-33).        b) Multidimensional Fatigue Questionnaire (MFI) for the evaluation of fatigue according to the Fatigue Intensity Scale (FIS) designed by Krupp and Associates (Krupp et al., “The fatigue severity scale. Application to patients with multiple sclerosis and systemic lupus erythematosus”, Arch Neurol. 1989; 46(10):1121-3).        c) Health and well-being questionnaire (SF36) (Ware J E, Jr., Sherbourne C D, “The MOS 36-item short-form health survey (SF-36). I. Conceptual framework and item selection”, Med Care 1992; 30:473-483; Bullinger M et al, “[SF-36 Health Survey in Rehabilitation Research. Findings from the North German Network for Rehabilitation Research, NVRF, within the rehabilitation research funding program]”, Rehabilitation (Stuttg). 2003, 42(4):218-25).        
The diagnostic methods most used today are based in large part on criteria with a significant subjective component, which often results in not having real certainty about whether or not a patient suffers from fibromyalgia. Moreover, not infrequently there are cases in which there are years of delay in diagnosing the disease, with the resultant detriment to the patient.
The lack of an objective diagnosis, along with a high and increasing number of persons affected (2-5% of the population), causes frequent socio-occupational problems.
With respect to other types of diagnostic methods for the disease of fibromyalgia, an attempt is been made to establish some molecular marker of the disease. Thus, a scientific publication in which a microRNA is proposed as fibromyalgia marker forms part of the prior art, specifically the miRNA-145 (Bjersing et al., “Profile of Cerebrospinal microRNAs in Fibromyalgia”, PLOS One Oct. 25, 2013, DOI: 10.1371/journal.pone.0078762). Said analysis is carried out by extracting cerebrospinal fluid from the patient by lumbar puncture and analysis of the sample.
The microRNAs (miRNAs) are monocatenary RNA molecules, normally of about 20-25 nucleotides, which have the ability to regulate the expression of specific genes by means of their post-transcriptional silencing, as a result of the miRNA joining the messenger RNA in a region in which they are complementary, the pairing leading to the degradation of the messenger RNA. The microRNAs are coded in the genome and are initially formed, as is known, as pri-miRNA, which is a long molecule of bicatenary RNA with the ability to form hairpins by complementarity between internal regions of the molecule. The so-called precursor microRNA, pre-miRNA, is formed when the pri-miRNA is processed by the drosha enzyme, which cuts off or eliminates the bases of the hairpins, that is, the unpaired ends. The pre-miRNA is transported from the nucleus to the cytoplasm, where it is fragmented by the dicer enzyme, which cuts it to the final length of 20-25 nucleotides, after which the resulting duplex is separated, resulting in two monocatenary RNAs, one of which is the mature microRNA, which performs its silencing action integrated in the RISC complex.
The prefix “mir” followed by a hyphen and a number is often used to refer to microRNAs. It is common to differentiate the pre-miRNA from the mature form by capital letters, so that the abbreviation “mir-” corresponds to the pre-miRNA, while the abbreviation “miR-” indicates that a mature microRNA is referred to. An abbreviation making reference to the species is often used in the front; thus, for example “hsa” refers to human microRNAs, of Homo sapiens. 
Letters (a, b, c . . . ) are also often found after the numbering, which indicate that two microRNAs have nearly identical sequences, differing only in one or two nucleotides. There are also microRNAs the abbreviation of which ends with indications such as “-5p” or “-3p”, which distinguish the microRNAs that originate from opposite arms (from the end 5′ or from the end 3) of the same pre-miRNA.
Although criteria have been established for identifying and naming miRNAs (Ambros V., Barte B., Barte D. P., Burge C. B., Carrington J. C., Chen X., Dreyfuss g., Eddy S. r., Griffiths-Jones S., Marshall M., Matzke M., Ruvkun G. Tuschl T., “A uniform system for microRNA annotation”, RNA 2003 9(3):277-279), the names of the microRNAs can be modified with respect to those initially published as the relation between sequences becomes better understood. Thus, in the databases dedicated to microRNAs, the access number, which is unique for each microRNA, can be considered to be the stable unique identifier for an entry.
Research is being carried out on the usefulness of some miRNAs in diagnosing diseases, for differentiating different types of cancer, or even for acting on them. Thus, for example, the family of the international application published as WO2012048236 refers to the use of microRNAs as biomarkers for identifying family and non-family colorectal cancer, while the family of the application WO2013190091 refers to circulating microRNAs as markers for breast cancer. Moreover, the U.S. Pat. No. 8,173,611 refers to a method for reducing the proliferation of cancerous cells which comprises introducing into the cell a synthetic molecule of bicatenary RNA, in which one of the chains is identical to a mature microRNA selected from the group miR-16, miR-96, miR-101, miR-105, miR-124, miR-142, miR-147, miR-206 and miR-346, wherein the chain complementary to the mature microRNA contains a chemical modification that increases the activity of the active chain. In the case of fibromyalgia, the previously cited tests, performed in cerebrospinal fluid, involve an intent to evaluate possible usefulness of these molecules as markers of the disease.
Since the disease of fibromyalgia is a disease with a complex diagnosis, it would be very positive to find some safe method of objective diagnosis that would be easy to carry out and analyze, and which would facilitate confirmation of the final diagnosis. It would be especially interesting that the diagnosis were of the molecular type in order to avoid any type of external distortion. It would be particularly interesting if the analyzed sample were easily obtainable and easy to handle in clinical practice, as well as quick. The present invention resolves this problem.